Mounting holes are known to include drilled holes in concrete which have an undercut portion at the base. Expandable mounting elements are known to have an expansion sleeve member fitted around a mounting member, such as a stay bolt or stud. An expander cone member is located at the front end of a mounting member so that the expansion sleeve member may be driven onto the expander cone member. Objects may be secured to the rear end of the mounting element so that when the mounting element is secured in the hole, the object is held firmly by the mounting element against the concrete surface around the mounting hole.
It is known that expandable mounting elements are subject to corrosion. Corrosion prevention meausures have either been directed at making the mounting elements either corrosion resistant or made from a suitable resistant material. In general, steel mounting elements are used for heavy-duty fastenings. Galvanization is used for when the requirement for corrosion resistance is relatively low. The mounting elements are made of special steel when there are higher corrosion resistance requirements.
Such protective measures are often inadequate. Moisture and other aggressive media can still penetrate the cracks and gaps in the mounting hole and the expandable mounting element, thereby attacking the concrete reinforcement and attack the individual parts of the expandable mounting element as a result of contact corrosion. The latter problem can not be avoided completely even for expandable mounting elements made of special steel, because of practical considerations and because different manufacturing processes are required for each individual part of the expandable mounting element so that different types of special steels are used.